Após a atualização, o postgresql 8.1 para 9.0 percebeu problemas com a dependência de bibliotecas. O Postgresql funciona bem (conexão, consultas).

yum list postgresql*
Installed Packages
postgresql.i386 9.0.0-1PGDG.el5 installed
postgresql-debuginfo.i386 9.0.0-1PGDG.el5 installed
postgresql-devel.i386 9.0.0-1PGDG.el5 installed
postgresql-libs.i386 9.0.0-1PGDG.el5 installed
postgresql-odbcng.i386 0.90.101-2.el5 installed
postgresql-plruby.i386 0.5.1-5.el5 installed
postgresql-server.i386 9.0.0-1PGDG.el5 install

mas quando estou tentando instalar 'pg' para ruby, eu recebi

gem install pg
Building native extensions.  This could take a while...
ERROR:  Error installing pg:
        ERROR: Failed to build gem native extension.

/usr/local/bin/ruby extconf.rb
checking for pg_config... no
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Ao tentar com outro driver ruby-postgres, eu tenho

yum install ruby-postgres
ruby-postgres-0.7.1-5.el5.i386 from epel has depsolving problems
  --> Missing Dependency: libpq.so.4 is needed by package ruby-postgres-0.7.1-5.el5.i386 (epel)

e

locate libpq.so.4
/usr/lib/libpq.so.4
/usr/lib/libpq.so.4.1

caminho também exportado

LD_LIBRARY_PATH=/usr/pgsql-9.0/lib
export LD_LIBRARY_PATH

depois de rodar o script ruby com "require pg" (funciona no 8.1), o ive obteve:

/usr/local/lib/ruby/site_ruby/1.8/i686-linux/pg_ext.so: libpq.so.4: cannot open shared object file: No such file or directory - /usr/local/lib/ruby/site_ruby/1.8/i686-linux/pg_ext.so (LoadError)
        from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:29:in `require'
        from /usr/local/lib/ruby/site_ruby/1.8/pg.rb:12
        from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:29:in `gem_original_require'
        from /usr/local/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:29:in `require'

Alguma sugestão do que fazer mais?